Recording control apparatus, recording and reproduction apparatus, and recording control method

ABSTRACT

A recording control apparatus includes a waveform rectification section for receiving a digital signal generated from an analog signal representing information reproduced from an information recording medium, and rectifying a waveform of the digital signal; a maximum likelihood decoding section for performing maximum likelihood decoding of the digital signal having the waveform thereof rectified, and generating a binary signal representing a result of the maximum likelihood decoding; a reliability calculation section for calculating a reliability of the result of the maximum likelihood decoding based on the digital signal having the waveform thereof rectified and the binary signal; and an adjusting section for adjusting a shape of a recording signal for recording the information on the information recording medium based on the calculated reliability.

This non-provisional application claims priority under 35 U.S.C.,§119(a), on Patent Application No. 2003-108821 filed in Japan on Apr.14, 2003, the entire contents of which are hereby incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a recording control apparatus, arecording and reproduction apparatus, and a recording control methodusing a maximum likelihood decoding method.

2. Description of the Related Art

In recording and reproduction apparatuses for recording original digitalinformation on, or reproducing such information from, a portablerecording medium, there can be a variance in the shape of marks formedon the medium among individual apparatuses or recording mediums evenwith an identical shape of recording pulse. This results in significantdifference in the quality of the signal reproduced. In order to avoidreduction in the reliability due to the variance, a correction operationis performed when, for example, the recording medium is mounted. Acorrection operation is a control operation for optimizing the settingof characteristics of the reproduction system, the shape of therecording pulse, or the like, in order to guarantee the reliability ofuser data.

A general information reproduction apparatus includes a PLL circuit forextracting clock information included in a reproduction signal andidentifying the original digital information based on the clockinformation extracted.

FIG. 14 shows a conventional optical disc drive. Light reflected by anoptical disc 17 is converted into a reproduction signal by an opticalhead 18. The reproduction signal is shape-rectified by a waveformequalizer 19. The resultant reproduction signal is binarized by acomparator 20. Usually, the threshold of the comparator 20 isfeedback-controlled such that an accumulation result of binary signaloutputs is 0. A phase comparator 21 obtains phase errors between thebinary signal outputs and the reproduction clocks. The phase errors areaveraged by an LPF 22, and a control voltage of a VCO 23 is determinedbased on the processing result. The phase comparator 21 isfeedback-controlled such that the phase errors output by the phasecomparator 21 are always 0. In recording mediums on which information isthermally recorded, the shape of the marks formed thereon vary inaccordance with the thermal interference of the mediums and recordingpatterns before and after the mark which is to be recorded. Therefore, arecording parameter which is optimal for the recording of each patternneeds to be set.

The above-described error detection output is an index for evaluatingthe recording parameter. The recording parameter is set such that theerror detection output is as small as possible. Specifically, arecording compensation circuit 27 generates a pulse having a prescribedpattern based on a recording pattern which is output from a patterngeneration circuit 26 using an initially set recording parameter. Alaser driving circuit 28 records information on the optical disc. Whileinformation is being reproduced from a track having the prescribedpattern recorded thereon, an error detection circuit 24 accumulatesabsolute values of phase errors between an output from the comparator 20and an output from the VCO 23, and thus obtains a detection signal. Thedetection signal is correlated with jitter between a reproduction clockand a binarized pulse edge. Recording and reproduction are repeatedlyperformed with different recording parameters. The recording parameterused when the detection value is minimal is determined as an optimalrecording parameter.

FIG. 15 shows a specific operation of the error detection circuit 24.Here, a recording pattern having a repetition of 6T, 4T, 6T and 8T isused. The mark termination edge corresponding to a pattern of acombination of 4T marks and 6T spaces is optimized. It is assumed that amark start edge corresponding to a pattern of a combination of 6T spacesand 8T marks, and a mark termination edge corresponding to a pattern ofa combination of 8T marks and 6T spaces, are recorded with an optimalrecording parameter.

When given an NRZI signal having a period shown in part (a) of FIG. 15,the recording compensation circuit 27 generates a laser waveform pulseshown in part (b) of FIG. 15. Tsfp is a parameter for setting a markstart position, and Telp is a parameter for setting a mark terminationposition. The laser driving circuit 28 modulates light emitting power inaccordance with the pattern shown in part (b) of FIG. 15. An amorphousarea is physically formed on the track as shown in part (c) of FIG. 15by laser light. When Telp is varied as Telp1, Telp2 and Telp3, the shapeof the mark formed is changed as shown in part (c) of FIG. 15.Information reproduction from the track having such marks will bediscussed.

When the recording parameter at the end of the 4T mark is Telp2, whichis the optimal value, a reproduction signal shown with a solid line inpart (d) of FIG. 15 is obtained. The threshold value is defined suchthat the accumulation value of the outputs from the comparator 20 is 0.A phase difference between the output from the comparator 20 and thereproduction clock is detected, and a reproduction clock (part (e) ofFIG. 15) is generated such that the accumulation value of the phaseerrors is 0.

In the case where the recording parameter at the end of a 4T mark ismade Telp1, which is smaller than the optimal value, a reproductionsignal shown in part (f) of FIG. 15 with the solid line is obtained.Since the termination edge of the 4T mark changes in a time axisdirection, the threshold value Tv of the comparator 20 is greater thanin the reproduction signal shown in part (d) of FIG. 15, as indicated bythe one-dot chain line in part (f) of FIG. 15. Because of the change inthe output from the comparator 20, the phase of the reproduction clockis advanced as compared to a reproduction clock shown in part (e) ofFIG. 15 such that the accumulation value of the phase errors is 0. As aresult, a reproduction clock shown in part (g) of FIG. 15 is generated.

In the case where the recording parameter at the end of a 4T mark ismade Telp3, which is greater than the optimal value, a reproductionsignal shown in part (h) of FIG. 15 with the solid line is obtained.Since the termination edge of the 4T mark changes in a time axisdirection, the threshold value Tv of the comparator 20 is smaller thanin the reproduction signal shown in part (d) of FIG. 15, as indicated bythe one-dot chain line in part (h) of FIG. 15. Because of the change inthe output from the comparator 20, the phase of the reproduction clockis behind as compared to a reproduction clock shown in part (e) of FIG.15 such that the accumulation value of the phase errors is 0. As aresult, a reproduction clock shown in part (i) of FIG. 15 is generated.

Measurement results of the time difference between the mark terminationedge (rising edge of a reproduction signal) and the reproduction clock(so-called data-clock jitter) exhibit distributions shown in parts (j)through (l) of FIG. 15. It is assumed here that the 4T mark terminationedge and the 8T mark termination edge have a variance such that both ofthe edges exhibit normal distributions of identical variance values.

In the case of the reproduction signal shown in part (d) of FIG. 15, andthe reproduction clock shown in part (e) of FIG. 15, the time differencedistribution between the output from the comparator 20 and thereproduction clock at the mark termination edge (rising edge) is asshown in part (k) of FIG. 15. The average value of the distributedvalues at the 4T mark termination edge, and the average value of thedistributed values at the 8T mark termination edge, are each 0.

In the case where the recording parameter of the end of the 4T mark isTelp1 (smaller than the optimal value Telp2), neither the average valueof the distributed values at the 4T mark termination edge, nor theaverage value of the distributed values at the BT mark termination edge,is 0, but both are away from 0 by the same distance, as shown in part(j) of FIG. 15. Therefore, the total variance at the rising edge isgreater than the case in part (k) of FIG. 15.

In the case where the recording parameter of the end of the 4T mark isTelp3 (greater than the optimal value Telp2), neither the average valueof the distributed values at the 4T mark termination edge, nor theaverage value of the distributed values at the 8T mark termination edge,is 0, but both are away from 0 by the same distance, as shown in part(l) of FIG. 15. In part (j) and part (l) of FIG. 15, the distribution ofthe 4T mark termination edge and the distribution of the BT marktermination edge are inverted. In this case also, the total variance atthe rising edge is greater than the case in part (k) of FIG. 15.

In the case where the accumulation result of absolute values of phaseerrors is the error detection output, the error detection value changesas shown in part (m) of FIG. 15 in accordance with the change in therecording parameter Telp. Accordingly, the recording parameter isvaried, and the recording parameter when the output from the errordetection circuit 24 is minimal is determined as an optimal recordingparameter.

In the above example, the recording parameter Telp at the 4T marktermination edge is optimized. For the other recording parameters, testrecordings using a respective specific parameter are performed and theoptimal recording parameters are obtained based on the error detectionoutput.

FIG. 16 is a flowchart illustrating an operation for obtaining all therecording parameters in accordance with the above-described procedure.Areas of a medium on which test recordings are to be performed areaccessed (S161), and the test recordings are performed while therecording parameter at the mark start edge or the mark termination edgeis changed prescribed area by prescribed area (for example, sector bysector)(S163). Information is reproduced from the test recording areas,and error detection outputs are obtained area by area by which therecording parameter is changed (S164). The recording parameter at whichthe error detection output is minimal is determined as an optimalparameter (S165). This operation is repeated until all the optimalparameters are obtained (S162) (see Japanese Laid-Open Publications Nos.2000-200418 and 2001-109597).

The above-described method by which the recording parameter is set suchthat the jitter is minimal has the following problem. In a systemadopting the maximum likelihood decoding method, the probability oferror generation is not necessarily minimal. Typically by the maximumlikelihood decoding method, a signal pattern is estimated from areproduction signal waveform, and a reproduction signal waveform and theestimated signal waveform are compared with each other, so that thereproduction signal is decoded into a signal having a signal patternwhich has the maximum likelihood. By the maximum likelihood decodingmethod, the probability of error generation is lower as the differencebetween the reproduction signal waveform and the estimated signalwaveform is smaller.

SUMMARY OF THE-INVENTION

According to one aspect of the invention, a recording control apparatusincludes a waveform rectification section for receiving a digital signalgenerated from an analog signal representing information reproduced froman information recording medium, and rectifying a waveform of thedigital signal; a maximum likelihood decoding section for performingmaximum likelihood decoding of the digital signal having the waveformthereof rectified, and generating a binary signal representing a resultof the maximum likelihood decoding; a reliability calculation sectionfor calculating a reliability of the result of the maximum likelihooddecoding based on the digital signal having the waveform thereofrectified and the binary signal; and an adjusting section for adjustinga shape of a recording signal for recording the information on theinformation recording medium based on the calculated reliability.

In one embodiment of the invention, the adjusting section adjusts ashape of a prescribed portion of the recording signal.

In one embodiment of the invention, the adjusting section adjusts aposition of an edge of the recording signal.

In one embodiment of the invention, the maximum likelihood decodingsection performs maximum likelihood decoding using a state transitionrule which is defined by a recording symbol having a minimum polarityinversion interval of 2 and an equalization system PR (C0,C1,C0).

In one embodiment of the invention, the maximum likelihood decodingsection performs maximum likelihood decoding using a state transitionrule which is defined by a recording symbol having a minimum polarityinversion interval of 2 and an equalization system PR (C0,C1,C1,C0).

In one embodiment of the invention, the maximum likelihood decodingsection performs maximum likelihood decoding using a state transitionrule which is defined by a recording symbol having a minimum polarityinversion interval of 2 and an equalization system PR (C0,C1,C2,C1,C0).

In one embodiment of the invention, the reliability calculation sectioncalculates the reliability based on a digital signal corresponding to anend of a recording mark formed on the information recording medium and abinary signal.

In one embodiment of the invention, the adjusting section adjusts theshape of the recording signal so as to improve the reliability.

In one embodiment of the invention, the adjusting section calculates oneof an accumulation value of the calculated reliability and an averagevalue of the calculated reliability, and adjusts the shape of therecording signal based on one of the accumulation value and the averagevalue.

In one embodiment of the invention, the adjusting section calculates oneof the accumulation value of the calculated reliability and the averagevalue of the calculated reliability for each of combinations of arecording mark length and a space length.

According to another aspect of the invention, a recording andreproduction apparatus includes a reproduction section for generating adigital signal from an analog signal representing information reproducedfrom an information recording medium; a waveform rectification sectionfor receiving the digital signal and rectifying a waveform of thedigital signal; a maximum likelihood decoding section for performingmaximum likelihood decoding of the digital signal having the waveformthereof rectified, and generating a binary signal representing a resultof the maximum likelihood decoding: a reliability calculation sectionfor calculating a reliability of the result of the maximum likelihooddecoding based on the digital signal having the waveform thereofrectified and the binary signal; an adjusting section for adjusting ashape of a recording signal for recording the information on theinformation recording medium based on the calculated reliability; and arecording section for recording the information on the informationrecording medium based on the adjusting result of the shape of therecording signal.

According to still another aspect of the invention, a recording controlmethod includes the steps of receiving a digital signal generated froman analog signal representing information reproduced from an informationrecording medium, and rectifying a waveform of the digital signal;performing maximum likelihood decoding of the digital signal having thewaveform thereof rectified, and generating a binary signal representinga result of the maximum likelihood decoding; calculating a reliabilityof the result of the maximum likelihood decoding based on the digitalsignal having the waveform thereof rectified and the binary signal; andadjusting a shape of a recording signal for recording the information onthe information recording medium based on the calculated reliability.

In one embodiment of the invention, the step of adjusting includes thestep of adjusting a shape of a prescribed portion of the recordingsignal.

In one embodiment of the invention, the step of adjusting includes thestep of adjusting a position of an edge of the recording signal.

Thus, the invention described herein makes possible the advantages ofproviding a recording control apparatus, a recording and reproductionapparatus, and a recording control method for optimizing a recordingparameter when recording information, such that the probability of errorgeneration at the time of maximum-likelihood decoding is minimal.

These and other advantages of the present invention will become apparentto those skilled in the art upon reading and understanding the followingdetailed description with reference to the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a structure of a recording and reproduction apparatusaccording to an example of the present invention;

FIG. 2 shows the state transition rule based on a combination of arecording symbol having a minimum polarity inversion interval of 2 andthe equalization system of PR (1,2,2,1) according to an example of thepresent invention;

FIG. 3 shows a trellis diagram corresponding to the state transitionrule shown in FIG. 2;

FIGS. 4A and 4B show distributions of Pa−Pb, which indicates thereliability of the maximum likelihood decoding according to an exampleof the present invention;

FIGS. 5A through 5S show 8 specific patterns used in an example of thepresent invention;

FIGS. 6A and 6B show the correlation between the reproduction waveformand the shift of a recording mark of Pattern-1 when path A is thecorrect path, Pa−1 being one of the 8 specific paths;

FIGS. 7A and 7B show the correlation between the reproduction waveformand the shift of a recording mark of Pattern-1 when path B is thecorrect path, Pa−1 being one of the 8 specific paths;

FIG. 8 is a table showing a list of recording parameters which should beoptimized;

FIG. 9 is a table showing which patterns out of the 8 patterns shown inFIG. 5 is used for detecting the recording patterns shown in FIG. 8;

FIG. 10 shows an edge shift detection circuit according to an example ofthe present invention;

FIG. 11 is a timing diagram illustrating an operation of the edge shiftdetection circuit shown in FIG. 10;

FIG. 12 shows a recording pattern for learning according to an exampleof the present invention;

FIG. 13 shows another edge shift detection circuit according to anexample of the present invention;

FIG. 14 shows a conventional optical disc drive;

FIG. 15 is a timing diagram illustrating an operation of a conventionalerror detection circuit;

FIG. 16 is a flowchart illustrating a conventional operation forobtaining a recording parameter;

FIG. 17 shows state transition rule based on a combination of arecording symbol having a minimum polarity inversion interval of 2 andthe equalization system of PR (a,b,a) according to an example of thepresent invention; and

FIG. 18 shows state transition rule based on a combination of arecording symbol having a minimum polarity inversion interval of 2 andthe equalization system of PR (a,b,c,b,a) according to an example of thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the present invention will be described by way ofillustrative examples with reference to the accompanying drawings.

First, a method for evaluating the quality of a reproduction signalobtained by using a maximum likelihood decoding method will bedescribed. In the following example, a recording symbol having a minimumpolarity inversion interval of 2 is used, and the waveform of the signalis rectified such that the frequency characteristic of the signal at thetime of recording and reproduction matches PR (1, 2, 2, 1).

Where the instant recording symbol is b_(k), the immediately previousrecording signal is b_(k−1), the recording signal two times previous isb_(k−2), and the recording signal three times previous is b_(k−3), anideal output value Level_(v) matching PR (1,2,2,1) is represented byexpression 1.Level _(v) =b _(k−3)+2b _(k−2)+2b _(k−1) +b _(k)  expression 1

-   -   where k is an integer representing the time, and v is an integer        of 0 through 6.

Where the state at time k is S(b_(k−2), b_(k−1), b_(k)), the statetransition table (Table 1) is obtained, TABLE 1 State transitions basedon a combination of a recording symbol having a minimum polarityinversion interval of 2T and the equalization system of PR (1, 2, 2, 1)State at time k − 1 State at time k S(b_(k−3), b_(k−2), b_(k−1))S(b_(k−2), b_(k−1), b_(k)) B_(k)/Level_(v) S(0, 0, 0) S(0, 0, 0) 0/0S(0, 0, 0) S(0, 0, 1) 1/1 S(0, 0, 1) S(0, 1, 1) 1/3 S(0, 1, 1) S(1, 1,0) 0/4 S(0, 1, 1) S(1, 1, 1) 1/5 S(1, 0, 0) S(0, 0, 0) 0/1 S(1, 0, 0)S(0, 0, 1) 1/2 S(1, 1, 0) S(1, 0, 0) 0/3 S(1, 1, 1) S(1, 1, 0) 0/5 S(1,1, 1) S(1, 1, 1) 1/6

Where, for simplicity, state (0,0,0)_(k) at time k is S0_(k), state(0,0,1)_(k) at time k is S1_(k), state (0,1,1)_(k) at time k is S2_(k),state (1,1,1)_(k) at time k is S3_(k), state (1,1,0)_(k) at time k isS4_(k), and state (1,0,0)_(k) at time k is S5_(k), the state transitiondiagram shown in FIG. 2 is obtained. The state transition diagram shownin FIG. 2 represents the state transition rule defined by the minimumpolarity inversion interval of 2 and the equalization system of PR(1,2,2,1). By developing this state transition diagram along the timeaxis, the trellis diagram shown in FIG. 3 is obtained. Now, state S0_(k)at time k and state S0_(k−4) at time k−4 will be discussed. FIG. 3 showstwo states transition paths which can be present between state S0_(k)and state S0_(k−4). Where one of such state transition paths is path A,path A follows states S2_(k−4), S4_(k−3), S5_(k−2), S0_(k−1) and S0_(k).Where the other one of such state transition paths is path B, path Bfollows states S2_(k−4), S3_(k−3), S4_(k−2), S5_(k−1) and S0_(k). Here,the maximum likelihood decoding result from time k−6 to time k is(C_(k−6), C_(k−5), C_(k−4), C_(k−3), C_(k−2), C_(k−1), C_(k)). When thedecoding result of (C_(k−6), C_(k−5), C_(k−4), C_(k−3), C_(k−2),C_(k−1), C_(k))=(0,1,1,x,0,0,0) is obtained where x is 0 or 1, the statetransition path A or B is estimated to have the maximum likelihood. PathA and path B have the same level of likelihood that the state at timek−4 is state S2_(k−4). Therefore, which of path A or path B has themaximum likelihood can be determined by finding an accumulation value ofsquares of the differences between (i) the value from reproductionsignal y_(k−3) to reproduction signal y_(k) from time k−3 to time k and(ii) the expected value of path A or the expected value of path B. Wherethe accumulation value of squares of the differences between (i) thevalue from reproduction signal y_(k−3) to reproduction signal y_(k) fromtime k−3 to time k and (ii) the expected value of path A is Pa, Pa isrepresented by expression 2. Where the accumulation value of squares ofthe differences between (i) the value from reproduction signal y_(k−3)to reproduction signal y_(k) from time k−3 to time k and (ii) theexpected value of path B is Pb, Pb is represented by expression 3.Pa=(y _(k−3)−4)²+(y _(k−2)3)²+(y _(k−1)−1)²+(y _(k−0))²  expression 2Pb=(y _(k−3)−5)²+(y _(k−2)−5)²+(y _(k−1)−3)²+(y _(k−1))²  expression 3

The difference between Pa and Pb (i.e., Pa−Pb), which represents thereliability of the maximum likelihood decoding result, has the followingmeaning. A maximum likelihood decoding section selects path A withconfidence when Pa<<Pb, and selects path B with confidence when Pa>>Pb.When Pa=Pb, there is no abnormality found in selecting either path A orpath B. The probability that the decoding result is correct is 50%. Byfinding Pa−Pb from the decoding result corresponding to a prescribedtime or a prescribed number of times, distributions of Pa−Pb as shown inFIGS. 4A and 4D is obtained.

FIG. 4A shows a distribution of Pa−Pb when noise is superimposed on thereproduction signal. The distribution has two peaks of frequency. Onepeak is when Pa=0, and the other peak is when Pb=0. Here, the value ofPa−Pb when Pa=0 is represented as −Pstd, and the value of Pa−Pb whenPb=0 is represented as Pstd. The absolute value of Pa−Pb is calculated,and |Pa−Pb|−Pstd is obtained.

FIG. 4B shows a distribution of |Pa−Pb|−Pstd. The standard deviation aand the average value Pave of the distribution shown in FIG. 4B areobtained. Where the distribution shown in FIG. 4B is a normaldistribution and, for example, the state where the value of thereliability of decoding result |Pa−Pb| is −Pstd or less is the statewhere an error has occurred, the error probability P (σ, Pave) isrepresented by expression 4 using σ and Pave. The error probability isthe probability at which the post-decoding reproduction signal isincorrect. $\begin{matrix}{{P\left( {\sigma,{Pave}} \right)} = {{erfc}\left( \frac{{Pstd} + {Pave}}{\sigma} \right)}} & {{expression}\quad 4}\end{matrix}$

An error probability of the binary signal representing the maximumlikelihood decoding result can be predicted from the average value Paveand the standard deviation a which are calculated from the distributionof Pa−Pb. Namely, the average value Pave and the standard deviation acan be an index of the quality of the reproduction signal. In the aboveexample, the distribution of |Pa−Pb| is assumed to be a normaldistribution. In the case where the distribution is not a normaldistribution, the number of times that the value of |Pa−Pb|−Pstd becomesless than or equal to a prescribed reference value is counted. Theobtained number can be an index of the quality of the reproductionsignal.

In the case of the state transition rule defined by the recording symbolhaving a minimum polarity inversion interval of 2 and the equalizationsystem PR (1,2,2,1), there are two possible state transition paths inthe following—number of state transition-patterns: 8-patterns from timek−4 to time k; 8 patterns from time k−5 to time k; and 8 patterns fromtime k−6 to time k. In a wider range of detection, there are Pa−Pbpatterns, which is the level of reliability. It is preferable to use thereliability Pa−Pb as the index of the quality of the reproductionsignal. In this case, it is not necessary to detect all the patterns; byonly detecting the patterns having a high error probability, such adetection result can be used as the index which is correlated with theerror probability. A pattern having a high error probability is apattern having a small value of reliability Pa−Pb. There are 8 suchpatterns, where Pa−Pb=±10. These 8 patterns and Pa−Pb are summarized inTable 2. TABLE 2 Patterns in which there can be two shortest statetransition paths Reliability of decoding result (Pa − Pb) Statetransition Pa = 0 Pb = 0 S2_(k−4) → S0_(k) −10 +10 S3_(k−4) → S0_(k) −10+10 S2_(k−4) → S1_(k) −10 +10 S3_(k−4) → S1_(k) −10 +10 S0_(k−4) →S4_(k) −10 +10 S5_(k−4) → S4_(k) −10 +10 S0_(k−4) → S3_(k) −10 +10S5_(k−4) → S3_(k) −10 +10

Based on the reliability Pa−Pb of the decoding results in theabove-mentioned 8 patterns, express on 5 is obtained.

Pattern-1When (C _(k−6) ,C _(k−5) ,C _(k−4) ,C _(k−3) ,C _(k−2) ,C _(k−1) ,C_(k))=(0,1,1,x,0,0,0),Pa−Pb=(E _(k−3) −F _(k−3))+(D _(k−2) −F _(k−2))+(B_(k−1) −D _(k−1))+(A _(k) −B _(k))Pattern-2When (C _(k−6) ,C _(k−5) ,C _(k−4) ,C _(k−3) ,C _(k−2) ,C _(k−1) ,C_(k))=(1,1,1,x,0,0,0),Pa−Pb=(F _(k−3) −G _(k−3))+(D _(k−2) −F _(k−2))+(B_(k−1) −D _(k−1))=(A _(k) −B _(k))Pattern-3When (C _(k−6) ,C _(k−5) ,C _(k−4) ,C _(k−3) ,C _(k−2) ,C _(k−1) ,C_(k))=(0,1,1,x,0,0,1),Pa−Pb=(E _(k−3) −F _(k−3))+(D _(k−2) −F _(k−2))+(B_(k−1) −D _(k−1))=(B _(k) −C _(k))Pattern-4When (C _(k−6) ,C _(k−5) ,C _(k−4) ,C _(k−3) ,C _(k−2) ,C _(k−1) ,C_(k))=(1,1,1,x,0,0,1),Pa−Pb=(F _(k−3) −G _(k−3))+(D _(k−2) −F _(k−2))+(B_(k−1) −D _(k−1))=(B _(k) −C _(k))Pattern-5When (C _(k−6) ,C _(k−5) ,C _(k−4) ,C _(k−3) ,C _(k−2) ,C _(k−1) ,C_(k))=(0,0,0,x,1,1,0),Pa−Pb=(A _(k−3) −B _(k−3))+(B _(k−2) −D _(k−2))+(D_(k−1) −F _(k−1))+(E _(k) −F _(k))Pattern-6When (C _(k−6) ,C _(k−5) ,C _(k−4) ,C _(k−3) ,C _(k−2) ,C _(k−1) ,C_(k))=(1,0,0,x,1,1,0),Pa−Pb=(B _(k−3) −C _(k−3))+(B _(k−2) −D _(k−2))+(D_(k−1) −F _(k−1))+(E _(k) −F _(k))Pattern-7When (C _(k−6) ,C _(k−5) ,C _(k−4) ,C _(k−3) ,C _(k−2) ,C _(k−1) ,C_(k))=(0,0,0,x,1,1,1),Pa−Pb=(A _(k−3) −B _(k−3))+(B _(k−2) −D _(k−2))+(D_(k−1) −F _(k−1))+(F _(k) −G _(k))Pattern-8When (C _(k−6) ,C _(k−5) ,C _(k−4) ,C _(k−3) ,C _(k−2) ,C _(k−1) ,C_(k))=(1,0,0,x,1,1,1),Pa−Pb=(B _(k−3) −C _(k−3))+(B _(k−2) −D _(k−2))+(D_(k−1) −F _(k−1))+(F _(k) −G _(k))  expression 5

Here, Ak=(yk−0), Bk=(yk−1)², Ck=(yk−2)², Dk=(yk−3)², Ek=(yk−4)²,Fk=(yk−5)², and Gk=(yk−6)². From the maximum likelihood decoding resultC_(k), Pa−Pb which fulfills expression 5 is obtained. From thedistribution of Pa−Pb, the standard deviation σ₁₀ and the average valuePave₁₀ are obtained. Where the distribution of Pa−Pb is assumed to be anormal distribution, the error probability P₁₀ is represented byexpression 6. $\begin{matrix}{{P_{10}\left( {\sigma_{10},{Pave}_{10}} \right)} = {{erfc}\left( \frac{10 + {Pave}_{10}}{\sigma_{10}} \right)}} & {{expression}\quad 6}\end{matrix}$

In the above-mentioned 8 patterns a 1-bit shift error occurs. In theother patterns, a 2- or more bit shift error occurs. A result ofanalysis of post-PRML processing error patterns shows that most of theerrors are 1-bit shift errors. Therefore, the error probability of thereproduction signal can be estimated by expression 6. In this manner,the standard deviation σ₁₀ and the average value Pave₁₀ can be used asthe index of the quality of the reproduction signal.

In this example of the present invention, the above-mentioned 8 patternsare detected for each recording pattern (for each combination of a marklength and a space length immediately before the mark, and for eachcombination of a mark length and a space length immediately after themark). A recording parameter for optimizing the position of the edge ofthe recording signal is determined, with specific attention paid to theshape of the recording signal, especially the mark start edge and themark termination edge. Paying attention only to the pattern having theminimum Pa−Pb value, among the reliability |Pa−Pb| of all the maximumlikelihood decoding results of all the patterns, means to pay attentiononly to the edge of a recording mark. As described above, a patternhaving a small value of Pa−Pb has a high error probability. This meansthat by partially optimizing the position of the edge of a recordingmark so as to improve the reliability of the maximum likelihood decodingresult, the entire recording parameter is optimized. A method foroptimizing the position of the edge of a recording mark will bedescribed hereinafter.

FIGS. 5A through 5H show sample values of 8 patterns (Pattern-1 throughPattern-8). The horizontal axis represents time. One scale representsone channel clock period (Tclk). The vertical axis represents signallevel (0 through 6). The dotted line represents path A, and the solidline represents path B. Each sample value corresponds to the expectedvalue Level_(v) 0 through 6 of the maximum likelihood decoding describedabove with reference to Table 1. As shown in part (c) and part (d) ofFIG. 15, a recorded portion (amorphous area) is represented as having asignal level below the threshold value of the comparator since the lightamount reflected by the recorded portion is lower than the light amountreflected by the other portions. An unrecorded portion (non-amorphousarea) is represented as having a signal level above the threshold valueof the comparator. The 8 patterns shown in FIGS. 5A through 5H eachcorrespond to a reproduction waveform of a border (mark start edge ormark termination edge) between the recorded portion (mark) and anunrecorded portion (space). Pattern-1, Pattern-2, Pattern-3, andPattern-4 each correspond to a mark start edge. Pattern-5, Pattern-6,Pattern-7, and Pattern-8 each correspond to a mark termination edge.

A method for detecting a shift of the mark start edge will be describedusing Pattern-1 as an example.

FIGS. 6A and 6B show the correlation between the reproduction waveformand the shift of a recording mark of Pattern-1. In FIGS. 6A and 6B, “A”represents an input signal. Path A represented by the dotted line is acorrect state transition path. The input signal is generated based on arecording mark B1. A recording mark A1 has an ideal position of the markstart edge. In FIG. 6A, the position of the mark start edge of therecording mark B1 is behind the ideal position. The sample value of theinput signal (y_(k−3), y_(k−2), y_(k−1), y_(k)) is (4.2, 3.2, 1.2, 0.2).From expressions 2 and 3, a distance Pa between the path A and the inputsignal, and a distance Pb between the path B and the input signal, areobtained by expressions 7 and 8, respectively.Pa=(4.2−4)²+(3.2⁻³)²+(1.2⁻¹)²+(0.2⁻⁰)²=0.16  expression 7Pb=(4.2−5)²+(3.2−5)²+(1.2−3)²+(0.2−1)²=7.76  expression 8

The amount and direction of the shift of the mark start edge areobtained by finding |Pa−Pb|−Pstd by expression 9.E1=|Pa−Pb|−Pstd=|0.16−7.76|−10=−2.4  expression 9

The absolute value of E1 obtained by expression 9 is the shift amount,and the sign of E1 is the shift direction. In the case of the recordingmark B1 in FIG. 6A, E1=−2.4. This means that the position of the markstart edge of the recording mark B1 is shifted rearward from thereference by 2.4.

In FIG. 6B, the position of the mark start edge of the recording mark B1is advanced to the ideal position. The sample value of the input signal(y_(k−3), y_(k-2), y_(k−1), y_(k)) is (3.8, 2.8, 0.8, −0.2). E2 isobtained by E2=|Pa−Pb|−Pstd. E2 is 2.4. This means that the position ofthe mark start edge of the recording mark B1 is shifted forward from thereference by 2.4.

FIGS. 7A and 7B show the correlation between the reproduction waveformand the shift of a recording mark of Pattern-1. In FIGS. 7A and 7B, pathB represented by the solid line is a correct state transition path. Herealso, “Δ” represents an input signal. The input signal is generatedbased on a recording mark B1. A recording mark A1 has an ideal positionof the mark start edge. In FIG. 7A, the position of the mark start edgeof the recording mark B1 is behind the ideal position. The sample valueof the input signal (y_(k−3), y_(k−2), y_(k−1), y_(k)) is (5.2, 5.2,3.2, 1.2). E3 is obtained by E3=|Pa−Pb|−Pstd. E3 is 2.4. This means thatthe position of the mark start edge of the recording mark B1 is shiftedrearward from the reference by 2.4. In FIG. 7B, the position of the markstart edge of the recording mark B1 is advanced to the ideal position.The sample value of the input signal (y_(k−3), y_(k−2), y_(k−1), y_(k))is (4.8, 4.8, 2.8, 0.8). E4 is obtained by E4=|Pa−Pb|−Pstd. E4 is −2.4.This means that the position of the mark start edge of the recordingmark B1 is shifted forward from the reference by 2.4.

Comparing the case of FIGS. 6A and 6B in which path A is the correctstate transition path and the case of FIGS. 7A and 7B in which path B isthe correct state transition path, the sign of the symbol representingthe shift direction is opposite. The sign of the symbol relies on therelationship between the expected value series of the correct statetransition path and, the input signal series, and the relationshipbetween the expected value series of the other candidate path and theinput signal series. When the error between the input signal and theexpected value of the incorrect candidate path is large as in FIG. 6Band FIG. 7A, the value obtained by expression 9 has a positive sign.Namely, as the difference between the input signal and the expectedvalue of the incorrect candidate path becomes larger, the errorprobability of the maximum likelihood decoding is lower. The shiftdirection of the position of the mark start edge of the recording markcan be detected in consideration of this. When path A is the correctstate transition path in Pattern-1, Pattern-1 is used for detecting thestart edge of the recording mark of a combination of a 2T space and a 4Tor longer mark. When path B is the correct state transition path inPattern-1, Pattern-1 is used for detecting the start edge of therecording mark of a combination of a 3T space and a 3T or longer mark.Using the above-described method, an accumulation value or an averagevalue of each recording pattern (i.e., each mark length/space lengthcombination) is obtained, and a recording parameter is set such that theshift amount of the position of the start edge and termination edge isclose to 0. Thus, a recording control optimal for the maximum likelihooddecoding method is realized.

Optimization of a recording parameter will be described. The minimumpolarity inversion interval of a recording symbol is represented by m(in this example, m=2). The position of the start edge of a recordingmark formed on an information recording medium may rely on the length ofthe space immediately before the recording mark and the length of therecording mark itself. For example, when the length of the spaceimmediately before the recording mark is mT to (m+b)T, the position ofthe mark start edge of the recording mark relies on the length of thespace immediately before the recording mark. When the length of thespace immediately before the recording mark is greater than (m+b) T, theposition of the mark start edge of the recording mark does not rely onthe length of the space immediately before the recording mark. When thelength of the recording mark itself to mT to (m+a)T, the position of themark start edge of the recording mark relies on the length of therecording mark itself. When the length of the recording mark itself isgreater than (m+a)T, the position of the mark start edge of therecording mark does not rely on the length of the recording mark itself.

The position of the termination edge of a recording mark formed on aninformation recording medium may rely on the length of the spaceimmediately after the recording mark and the length of the recordingmark itself. For example, when the length of the recording mark itselfis mT to (m+a)T, the position of the mark termination edge of therecording mark relies on the length of the recording mark itself. Whenthe length of the recording mark itself is greater than (m+a)T, theposition of the mark termination edge of the recording mark does notrely on the length of the recording mark itself. When the length of thespace immediately after the recording mark is mT to (m+b)T, the positionof the mark termination edge of the recording mark relies on the lengthof the space immediately after the recording mark. When the length ofthe space immediately after the recording mark is greater than (m+b)T,the position of the mark termination edge of the recording mark does notrely on the length of the space immediately after the recording mark. Inthe above, “a” and “b” are each an integer of 0 or greater, and theminimum polarity inversion interval of the recording symbol is greaterthan m+a and m+b.

In consideration of the position of the mark start edge and the positionof the mark termination edge of a recording mark, the optimization ofthe parameter Tsfp at the mark start edge needs to be performed on arecording mark adjacent to a space having a length of (m+b)T or less.The optimization of the parameter Telp at the mark termination edgeneeds to be performed on a recording mark having a length of (m+a)T orless. Where, for simplicity, m=3 and a=b=3, the parameter needs to beoptimized for 32 recording patterns shown in FIG. 8. In FIG. 8, 2Ts2Tm,for example, means a pattern in which a 2T space exists immediatelybefore a 2T mark.

FIG. 9 shows which pattern out of the 8 patterns (Pattern-1 throughPattern-8) is used for detecting the recording patterns (i.e., edgepatterns) shown in FIG. 8. For example, the shift amount of the signalcorresponding to a 2Ts3Tm-recording pattern (FIG. 8) is detected usingP3A (FIG. 9). P3A is Pattern-3 in which path A is the correct statetransition path. The shift amount of the signal of a 3Ts3Tm recordingpattern (FIG. 8) is detected using P1B or P4A (FIG. 9). P1B is aPattern-1 in which path B is the correct state transition path. P4A is aPattern-4 in which path A is the correct state transition path. As canbe appreciated from the above, a method for controlling a recordingparameter optimal for the maximum likelihood decoding method is tochange the recording parameter such that the shift amount of the signalcorresponding to every recording pattern shown in FIG. 9 is close to 0.

In FIG. 9, the shift amount of the signal corresponding to each of a2Ts2Tm recording pattern (a 2T space is present immediately before a 2Tmark) and a 2Tm2Ts (a 2T space is present immediately after a 2T mark)cannot be detected by any of the 8 patterns described above. Thus, theshift amount needs to be optimized by another method. However, the2Ts2Tm recording pattern and the 2Tm2Ts recording pattern have arelatively large value of reliability Pa−Pb and thus are not included inthe above 8 patterns. In other words, at the mark start edge or marktermination edge of the recording mark of each of the 2Ts2Tm recordingpattern and the 2Tm2Ts recording pattern, the error probability is low;it is not necessary to strictly optimize the recording parameter ofthese recording patterns. Therefore, an appropriate initial value may beused as the recording parameter instead of optimizing such shift amountsfor each information recording medium. Alternatively, the 2Ts2Tmrecording pattern and the 2Tm2Ts recording pattern may be optimized suchthat the accumulation value of the phase errors of the reproductionsignal is minimal.

FIG. 1 shows a recording and reproduction apparatus 100 according to anexample of the present invention. The recording and reproductionapparatus 100 executes the above-described method for optimizingrecording parameters.

The recording and reproduction apparatus 100 includes a reproductionsection 101, a recording control device 102, and a recording section103. On the recording and reproduction apparatus 100, an informationrecording medium 1 can be mounted. The information recording medium 1 isusable for optical information recording and reproduction, and is, forexample, an optical disc.

The reproduction section 101 includes an optical head section 2, apreamplifier 3, an AGC 4, a waveform equalizer 5, an A/D converter 6,and a PLL circuit 7. The reproduction section 101 generates a digitalsignal from an analog signal representing information reproduced fromthe information recording medium 1.

The recording control section 102 includes a rectification section 8, amaximum likelihood decoding section 9, a reliability calculation section10, and an adjusting section 104. The adjusting section 104 includes apattern detection circuit 11, an edge shift detection circuit 12, and aninformation recording medium controller 13. The recording controlsection 102 is produced as, for example, a semiconductor chip.

The rectification section 8 is, for example, a digital filter, andreceives the digital signal generated by the reproduction section 101and rectifies the waveform of the digital signal such that the digitalsignal has a prescribed equalizing characteristic.

The maximum likelihood decoding section 9 is, for example, a Veterbidecoding circuit, and performs maximum likelihood decoding of thedigital signal having the waveform thereof rectified by therectification section 8 and generates a binary signal representing theresult of the maximum likelihood decoding.

The reliability calculation section 10 is, for example, a differentialmetric detection circuit, and calculates the reliability of the resultof the maximum likelihood decoding based on the digital signal havingthe waveform thereof rectified by the rectification section 8 and thebinary signal output from the maximum likelihood decoding section 9. Inone embodiment of the present invention, the reliability calculationsection 10 calculates the reliability of the result of the maximumlikelihood decoding based on digital signals corresponding to a markstart edge and a mark termination edge of a recording mark formed on theinformation recording medium 1 and binary signals.

The adjusting section 104 adjusts the shape of prescribed portions of arecording signal for recording information on the information recordingmedium 1 based on the reliability calculated by the reliabilitycalculation section 10. The adjusting section 104 adjusts, for example,the positions of edges of the recording signal. The adjustment of theshape of the recording signal by the adjusting section 104 is performedsuch that the reliability of the result of the maximum likelihooddecoding is improved. The information recording medium controller 13 is,for example, an optical disc controller.

The recording section 103 includes a pattern generation circuit 14, arecording compensation circuit 15, a laser driving circuit 16, and anoptical head section 2. The recording section 103 records information onthe information recording medium 1 based on the adjusting result of theshape of the recording signal. In this example, the optical head section2 is included both in the reproduction section 101 and the recordingsection 103, and has both the functions of a recording head and areproduction head. The recording head and the reproduction head may beseparately provided. An operation of the recording and reproductionapparatus 100 will be described in detail below.

The optical head section 2 generates an analog reproduction signalrepresenting information which is read from the information recordingmedium 1. The analog reproduction signal is amplified and AC-coupled bythe preamplifier 3 and then is input to the AGC 4. The AGC 4 adjusts thegain of the analog reproduction signal such that the output from thewaveform equalizer 5, which will later process the signal, has aconstant amplitude. The analog reproduction signal which is output fromthe AGC 4 has the waveform thereof rectified by the waveform equalizer5. The resultant analog reproduction signal is output to the A/Dconverter 6. The A/D converter 6 samples the analog reproduction signalin synchronization with a reproduction clock which is output from thePLL circuit 7. The PLL circuit 7 extracts the reproduction clock from adigital reproduction signal obtained by sampling performed by the A/Dconverter 6.

The digital reproduction signal generated by sampling performed by theA/D converter 6 is input to the rectification section S. Therectification section 8 adjusts the frequency of the digitalreproduction signal (i.e., adjusts the waveform of the digitalreproduction signal), such that the frequency characteristic of thedigital reproduction signal is the characteristic assumed by the maximumlikelihood decoding section 9 (in this example, PR (1,2,2,1)equalization characteristic) at the time of recording and reproduction.

The maximum likelihood decoding section 9 performs maximum likelihooddecoding of the digital reproduction signal having the waveform thereofrectified by the rectification section 8, and thus generates a binarysignal. The reliability calculation section 10 receives the digitalreproduction signal having the waveform thereof rectified by therectification section 8 and the binary signal. The reliabilitycalculation section 10 identifies the state transition from the binarysignal, and obtains |Pa−Pb|−Pstd (see expression 9; hereinafter,referred to simply as “Pabs”) which represents the reliability of thedecoding result, based on the identification result and the branchmetric. Based on the binary signal, the pattern detection circuit 11generates a pulse signal for assigning the above-mentioned 8 patterns(Pattern-1 through Pattern-8) for each recording pattern shown in FIG.9, and outputs the pulse signal to the edge shift detection circuit 12.The edge shift detection circuit 12 accumulatively adds the reliabilityPabs pattern by pattern, and obtains a shift of the recordingcompensation parameter from the optimal value (i.e., an edge shift). Theinformation recording medium controller 13 changes the recordingparameter (waveform of the recording signal) which is determined to bechanged based on the edge shift amount added pattern by pattern. Thepattern generation circuit 14 outputs a recording compensation leaningpattern.

Based on the recording parameter from the information recording mediumcontroller 13, the recording compensation circuit 15 generates a laserlight emission waveform pattern in accordance with the recordingcompensation leaning pattern. In accordance with the resultant lightemission waveform pattern, the laser driving circuit 16 controls a laserlight emission operation of the optical head section 2.

Next, an operation of the edge shift detection circuit 12 in thisexample will be described in detail. FIG. 10 shows the pattern detectioncircuit 11 and the edge shift detection circuit 12. The edge shiftdetection circuit 12 receives a pattern detection result obtained by thepattern detection circuit 11 and the reliability Pabs calculated by thereliability calculation section 10. The reliability Pabs data input tothe edge shift detection circuit 12 is delayed by a flip-flop (FF) inconsideration of the delay caused by the pattern detection circuit 11.The reliability Pabs data corresponding to the pattern detection outputand the detection output point are input to an adder, and the patterndetection result is input to a selector. The selector selects theaccumulation-result obtained up to that point in accordance with thedetection pattern and inputs the selected-result to the adder. The adderadds the accumulation result and the newly input reliability Pabs data,and outputs the addition result. A specific register corresponding tothe detection pattern, when receiving an enable signal, stores theaddition result.

For example, in the case wherein formation is recorded on an informationrecording medium in which information is managed address by address, itis assumed to use an addition zone gate signal and a register enablesignal shown in part (b) and part (c) of FIG. 11. Part (a) of FIG. 11shows an address unit. In the case where test recording is performed ina user area address by address so as to obtain an edge shift amount, acontrol needs to be performed for defining an addition zone. When theaddition zone gate signal shown in part (b) of FIG. 11 is input to theedge shift detection circuit 12, the addition zone gate signal passesthrough the two-stage flip-flop shown in FIG. 10 and is input toflip-flops FF29 through FF0. The flip-flops are reset in a low zone ofthe addition zone gate signal shown in part (b) of FIG. 11, and theaddition result is stored in a high zone. The register enable signalshown in part (c) of FIG. 11 is generated from the addition zone gatesignal. The register enable signal is for storing the addition result toregisters REG29 through REG0 at the end of the addition zone gatesignal. Data representing the edge shift amount address by address isstored in the registers REG29 through REG0. The edge shift detectioncircuit 12, owing to such a circuit configuration, can obtain all theedge shift amounts necessary for optimization of the recording parameterusing one adder.

In the example shown in FIG. 10, the generation frequency of therecording patterns varies in accordance with the combination of theprescribed length of marks and spaces required for optimization of therecording parameter, among the recording patterns used for testrecording (e.g., random patterns). The 30 edge shift amounts detected(R23T, R33T, . . . R45L, R55L) rely on the generation frequency of therecording patterns.

The PLL circuit 7 shown in FIG. 1 automatically detects a thresholdvalue of a slicer (not shown) using a DC component (a low frequencycomponent included in the reproduction signal) and synchronizes thereproduction signal and the reproduction clock signal. Accordingly, itis preferable that the amount of the DC component included in the testrecording pattern is as small as possible, such that the feedbackcontrol does not influence the clock generation performed by the PLLcircuit 7. In consideration of the time required for optimization andprecision of optimization, it is preferable to obtain a detection resulthaving a high precision with a minimum possible recording area.Therefore, the following recording pattern is required: a recordingpattern which has mark length/space length combinations required foroptimization of the recording parameter at the same frequency, in whichthe code includes no DC component (DSV), and in which the generationfrequency, per unit area, of the mark length/space length combinationsrequired for optimization of the recording parameter to high. An exampleof such a recording pattern is shown in FIG. 12.

In FIG. 12, 2M represents a 2T mark, and 2S represents a 2T space. Inthis example, each of 30 patterns of combinations of 2T through 5T marksand 2T through 5T spaces is generated once in a 108-bit recordingpattern. The number of symbols “0” and the number of symbols “1”including the 108-bit recording pattern are both 54, and the DSV in therecording pattern is 0. By applying this recording pattern to the edgeshift detection circuit 12 in FIG. 10, each pattern can be detected thesame number of times. Thus, a more accurate shift amount detectionresult is obtained. In this example, it is assumed that 5T or longermarks or 5T or longer spaces can be recorded with the same recordingparameter.

FIG. 13 shows an edge shift detection circuit 12 a which is amodification of the edge shift detection circuit 12. In the edge shiftdetection circuit 12 a, random patterns are used for test recording.Namely, different test recording patterns are generated at differentfrequencies.

The pattern detection circuit 11 detects an edge of each of specificpatterns (30 patterns) shown in FIG. 9. The edge shift detection circuit12 a accumulates the edge shift amounts corresponding to each of thepatterns, and counts the number of times that each pattern has beendetected. By dividing each accumulation result of the edge shift amountswith the number of times that the respective pattern has been detected,the average edge shift amount of each specific pattern is obtained.Thus, even when random patterns are used for test recording, it can bedetermined which is the pattern corresponding to the recording markhaving the mark start edge position or the mark termination edgeposition which should be changed.

As described above, the edge shift detection circuit 12 included in theadjusting section 104 calculates one of is an accumulation value or anaverage value of the reliability of the maximum likelihood decodingresult for each recording pattern (i.e., for each mark length/spacelength combination) and adjusts the shape of the recording signal basedon the accumulation value or average value obtained.

In the above example, the state transition rule defined by the recordingsymbol having a minimum polarity inversion interval of 2 and theequalization system of PR (1,2,2,1) is used by the maximum likelihooddecoding section 9 for performing maximum likelihood decoding. Thepresent invention is not limited to this. The present invention isapplicable to use of, for example, a state transition rule defined bythe recording symbol having a minimum polarity inversion interval of 3and the equalization system of PR (C0,C1,C1,C0), a state transition ruledefined by the recording symbol having a minimum polarity inversioninterval of 2 or 3 and the equalization system of PR (C0,C1,C0), and astate transition rule defined by the recording symbol having a minimumpolarity inversion interval of 2 or 3 and the equalization system of PR(C0,C1,C2,C1,C0). C0, C1 and C2 are each an arbitrary positive numeral.

Table 3 shows the state transition rule defined by the recording symbolhaving a minimum polarity inversion interval of 2 and an equalizationsystem of PR (a,b,a). FIG. 17 shows a state transition diagramrepresenting the state transition rule. Here, “a” and “b” are each anarbitrary positive numeral. TABLE 3 State transitions based on acombination of a recording symbol having a minimum polarity inversioninterval of 2T and the equalization system of PR (a, b, a) State at timek − 1 Input at time k S(b_(k−3), b_(k−2), b_(k−1)) b_(k) Signal levelS(0, 0) 0 0 S(0, 0) 1 a S(0, 1) 1 a + b S(1, 0) 0 a S(1, 1) 0 a + bS(1, 1) 1 2a + b

Table 4 shows the state transition rule defined by the recording symbolhaving a minimum polarity inversion interval of 2 and an equalizationsystem of PR (a,b,c,b,a). FIG. 18 shows a state transition diagramrepresenting the state transition rule. Here, “a”, “b” and “c” are eachan arbitrary positive numeral. TABLE 4 State transitions based on acombination of a recording symbol having a minimum polarity inversioninterval of 2T and the equalization system of PR (a, b, c, b, a) Stateat time k − 1 Input at time k S(b_(k−4), b_(k−3), b_(k−2), b_(k−1))b_(k) Signal level S(0, 0, 0, 0) 0 0 S(0, 0, 0, 0) 1 A S(0, 0, 0, 1) 1a + b S(0, 0, 1, 1) 0 B + c S(0, 0, 1, 1) 1 a + b + c S(0, 1, 1, 0) 0B + c S(0, 1, 1, 1) 0 2b + c S(0, 1, 1, 1) 1 a + 2b + c S(1, 0, 0, 0) 0A S(1, 0, 0, 0) 1 2a S(1, 0, 0, 1) 1 2a + b S(1, 1, 0, 0) 0 A + b S(1,1, 0, 0) 1 2A + b S(1, 1, 1, 0) 0 A + b + c S(1, 1, 1, 1) 0 A + 2b + cS(1, 1, 1, 1) 1 2a + 2b + c

The maximum likelihood decoding section 9 may perform maximum likelihooddecoding using the state transition rules shown in Tables 3 and 4 andFIGS. 17 and 18.

In the above example, the recording parameter is for controlling theposition of the mark start edge and the position of the mark terminationedge of a recording mark. The present invention is not limited to this.In the case of performing laser light emission using a multiple pulsesignal described with reference to FIG. 15, a parameter for controllingthe width of a leading pulse, the width of a terminating pulse, or thewidth of a cooling pulse may be adjusted based on the reliability of themaximum likelihood decoding.

The elements of the recording and reproduction apparatus 100 may beimplemented by hardware or software. For example, an operation performedby at least one of the rectification section 8, the maximum likelihooddecoding section 9, the reliability calculation section 10, and theadjusting section 11 may be implemented by a computer-executableprogram.

According to the present invention, the reliability of the result of themaximum likelihood decoding is calculated based on the digital signalhaving the waveform thereof rectified and the binary signal generated bythe maximum likelihood decoding section. Based on the calculatedreliability, the shape of the recording signal for recording informationon the information recording medium is adjusted. Thus, the shape of therecording signal can be adjusted so as to improve the reliability of theresult of the maximum likelihood decoding, and thus the errorprobability at the time of maximum likelihood decoding can be reduced.

According to the present invention, a recording parameter which isoptimal for the maximum likelihood decoding method is set such that theerror probability is minimal when the signal is decoded using themaximum likelihood decoding method. The reliability of the result ofmaximum likelihood decoding is calculated for portions of a signal whichcorrespond to a mark start edge and a mark termination edge of arecording mark and have a high error probability by the maximumlikelihood decoding method. This calculation is performed for each ofmark length/space length combinations. Based on the calculation result,a recording parameter for optimizing the position of the mark start edgeand the position of the mark termination edge is obtained. Informationrecording is performed reflecting the recording parameter obtained. Byoptimizing the recording parameter of a portion of a recording signalhaving a high error probability at the time of maximum likelihooddecoding, the readability of the reproduced information can be improved.

As described above, the present invention is especially useful for arecording control apparatus, a recording and reproduction apparatus, anda recording control method using the maximum likelihood decoding method.

Various other modifications will be apparent to and can be readily madeby those skilled in the art without departing from the scope and spiritof this invention. Accordingly, it is not intended that the scope of theclaims appended hereto be limited to the description as set forthherein, but rather that the claims be broadly construed.

1. A recording control apparatus, comprising; a waveform rectificationsection for receiving a digital signal generated from an analog signalrepresenting information reproduced from an information recordingmedium, and rectifying a waveform of the digital signal; a maximumlikelihood decoding section for performing maximum likelihood decodingof the digital signal having the waveform thereof rectified, andgenerating a binary signal representing a result of the maximumlikelihood decoding; a reliability calculation section for calculating areliability of the result of the maximum likelihood decoding based onthe digital signal having the waveform thereof rectified and the binarysignal; and an adjusting section for adjusting a shape of a recordingsignal for recording the information on the information recording mediumbased on the calculated reliability.
 2. A recording control apparatusaccording to claim 1, wherein the adjusting section adjusts a shape of aprescribed portion of the recording signal.
 3. A recording controlapparatus according to claim 1, wherein the adjusting section adjusts aposition of an edge of the recording signal.
 4. A recording controlapparatus according to claim 1, wherein the maximum likelihood decodingsection performs maximum likelihood decoding using a state transitionrule which is defined by a recording symbol having a minimum polarityinversion interval of 2 and an equalization system PR (C0,C1,C0).
 5. Arecording control apparatus according to claim 1, wherein the maximumlikelihood decoding section performs maximum likelihood decoding using astate transition rule which is defined by a recording symbol having aminimum polarity inversion interval of 2 and an equalization system PR(C0,C1,C1,C0).
 6. A recording control apparatus according to claim 1,wherein the maximum likelihood decoding section performs maximumlikelihood decoding using a state transition rule which is defined by arecording symbol having a minimum polarity inversion interval of 2 andan equalization system PR (C0,C1,C2,C1,C0).
 7. A recording controlapparatus according to claim 1, wherein the reliability calculationsection calculates the reliability based on a digital signalcorresponding to an end of a recording mark formed on the informationrecording medium and a binary signal.
 8. A recording control apparatusaccording to claim 1, wherein the adjusting section adjusts the shape ofthe recording signal so as to improve the reliability.
 9. A recordingcontrol apparatus according to claim 1, wherein the adjusting sectioncalculates one of an accumulation value of the calculated reliabilityand an average value of the calculated reliability, and adjusts theshape of the recording signal based on one of the accumulation value andthe average value.
 10. A recording control apparatus according to claim9, wherein the adjusting section calculates one of the accumulationvalue of the calculated reliability and the average value of thecalculated reliability for each of combinations of a recording marklength and a space length.
 11. A recording and reproduction apparatus,comprising: a reproduction section for generating a digital signal froman analog signal representing information reproduced from an informationrecording medium; a waveform rectification section for receiving thedigital signal and rectifying a waveform of the digital signal; amaximum likelihood decoding section for performing maximum likelihooddecoding of the digital signal having the waveform thereof rectified,and generating a binary signal representing a result of the maximumlikelihood decoding; a reliability calculation section for calculating areliability of the result of the maximum likelihood decoding based onthe digital signal having the waveform thereof rectified and the binarysignal; an adjusting section for adjusting a shape of a recording signalfor recording the information on the information recording medium basedon the calculated reliability; and a recording section for recording theinformation on the information recording medium based on the adjustingresult of the shape of the recording signal.
 12. A recording controlmethod, comprising the steps of: receiving a digital signal generatedfrom an analog signal representing information reproduced from aninformation recording medium, and rectifying a waveform of the digitalsignal; performing maximum likelihood decoding of the digital signalhaving the waveform thereof rectified, and generating a binary signalrepresenting a result of the maximum likelihood decoding; calculating areliability of the result of the maximum likelihood decoding based onthe digital signal having the waveform thereof rectified and the binarysignal; and adjusting a shape of a recording signal for recording theinformation on the information recording medium based on the calculatedreliability.
 13. A recording control method according to claim 12,wherein the step of adjusting includes the step of adjusting a shape ofa prescribed portion of the recording signal.
 14. A recording controlmethod according to claim 12, wherein the step of adjusting includes thestep of adjusting a position of an edge of the recording signal.